Contact arm assembly for circuit interrupter



Aug. 13, 1957 R. G. PAGE ET AL CONTACT ARM ASSEMBLY FOR CIRCUIT INTERRUPTER Filed Sept. 15, 1954 s m f .m m M m D r M N aw. K Am & PH. w ma A 1 A M 0H RC 77///// ATTORNEY United States Patent ARM ASSEMBLY FOR CIRCUIT INTERRUPTER Application September 13, 1954, Serial No. 455,396

Claims. (Cl. 200-164) CONTACT Our invention relates to electric circuit interrupters, and more particularly to a contact arm assembly for circuit interrupters for supporting and moving a movable contact between open and closed circuit positions.

In switches and circuit breakers having separable contacts, it is necessary for proper operation that in the closed circuit position there shall be some force, preferably of a resilient nature, constantly pressing the contacts together. This force or contact pressure is necessary to ensure good electrical contact between the contact surfaces, and to prevent excessive heating. The force should be resilient in order to make up for Wear of the parts, including the contact surfaces, during normal use.

One of the simplest and most effective ways of providing such resilient contact pressure is to construct the contact supporting arm of resilient material, and to provide an operating mechanism such that in the closed circuit position the contact arm is slightly deformed, whereby its tendency to return to its normal condition supplies the needed contact pressure. This system is very suitable for devices of relatively low-current rating, but it has many drawbacks and limitations which restrict its use in circuit interrupters of high capacity. It requires, for instance, that the contact arm be made of a material having a relatively high degree of resilience. Such materials are not ordinarily the best electrical conductors. When such a contact arm is used to conduct a substantial amount of current to the movable contact, an undesirable voltage drop therethrough may result and, in addition, an excessive amount ofheat may be generated therein. While metallic alloys having high conductivity and also high resilience have been developed, they are relatively expensive,,and difficult to fabricate. The resilient contact-arm type of construction also requires that the shape or cross-section proportions of the contact arm be such as to facilitate the desired resilient deformation. Such shape or cross-section may be unsuitable in view of space limitations of the circuit interrupter casing, and particularly in view of the requirements of the arc extinguishing chamber'into which the contact arm must extend. p

A relatively rigid contact arm, on the other hand, may be readily constructed of high conductivity metal such as copper, and may be proportioned as desired in view of space requirements. The use of such a rigid contact arm makes it difficult, however, to obtain resilient contact pressure of deformation of the contact arm. Consequently, it ordinarily requires that a more complicated operating mechanism be provided or that one or both contacts be provided with separate resilient mounting means.

One-object of our invention, therefore, is to provide a contact arm construction for circuit interrupters which permits the use therefor of a rigid structure of high conductivity material but which construction also provides an inherent means for supplying contact pressure similar to that obtained from a resilient contact arm.

2,802,922 Patented Aug. 13, 1957 It is also desirable for the purpose of improving the operation of switches and circuit making and breaking devices, that a sliding or wiping action of the contacting surfaces take place during the making and breaking operations. Such sliding or Wiping contact surfaces are self-cleaning, since the wiping action rubs off dirt, oxide film, etc. Better electrical contact is also furnished since the contact surfaces are brought into more intimate contact over a greater area by the wiping action which tends to rub off high spots. It is desirable that such wiping action occur during opening as well as closing of the contacts. Electrical contact surfaces, especially those having a surface of highly conductive but comparatively low-melting point or non-refractory material, such as the commonly used silver and copper, occasionally stick together by reason of the fusing together of points on the surface thereof. A sliding action helps to break such welds and assures that the contacts will separate properly. Such a wiping action is not-ordinarily obtained, however, in circuit interrupters utilizing butt-type contacts, since the relative motion of such contacts is substantially perpendicular to the meeting contact surfaces.

Another object of our invention, therefore, is to provide a contact arm construction for use in circuit interrupters incorporating butt-type contacts which provides a sliding or wiping action of the contact surfaces and one which provides such sliding action during both the closing and opening operation.

It is also an object of our invention to provide a circuit interrupter having an improved sliding action of the contacts thereof, comprising a double wiping or reciprocating sliding action during both the making and breaking operations.

A further object of our invention is to provide a resilient contact arm construction for circuit interrupters which shall be inexpensive to manufacture and easy to assemble.

In carrying out our invention in one form, we provide a relatively rigid contact arm supported for movement including sliding movement in a circuit interrupter casin'g, a resilient member connected between the contact arm and the casing, and means for-applying contact closing force to the resilient member, whereby deformation of the resilient member by the application of such contact-closing force not only exerts the necessary contact-pressure, but also causes the contact arm to slide longitudinally a small amount after engagement of the contacts.

In accordance with a further feature of our invention, we provide a circuit interrupter having such a contact arm construction and also having means for applying contact-closing force to the resilient member in such a manner as to cause the contact arm to slide longitudinally in a reciprocating manner after contact engagement whereby a double wiping action is provided between the contact surfaces.

Our invention will be readily understood from the following-description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Figure 1 is a side elevation view of a circuit interrupter incorporating our invention, the casing being shown in section, and the mechanism being shown in the closed-circuit position.

Figure 2 is a view taken on the line 2-2 of Figure 1.

Figure 3 is a perspective view of some of the parts of the interrupter of Figure 1.

Figure 4 is a view of a portion of a mechanism of Figure 1 in the open-circuit position.

Referring to the drawing, we have shown our invention as embodied in a manually operable circuit interrupter, including an open-"sided insulating casing 1 provided with a side cover 2 adapted to be held thereon by suitable fastening means such as by rivets (not shown) passing through holes 3. The parts of the circuit interrupter are supported in suitable formed recesses in the said casing and cover, and include a line terminal 4, carrying a line terminal screw 5 at its outer end, and having a line contact 6 fastened to its inner end by suitable means, such as by welding. A load terminal 7 is provided, carrying a load terminal screw 8 on its outer end and having a flexible conductive braid 9 attached to its inner end, which braid is also attached to a movable contact arm 10. The movable contact arm 10 is pivotally and slidably supported in the casing by means of a fixed pivot pin 11 which is supported at its ends in suitable recesses in the casing 1 and which passes through an elongated opening 30 in the contact arm. The arm 10 carries a movable contact 12 fixedly attached to its free end. The current path therefor may be traced through the circuit interrupter when in the closed-circuit position as follows-from line terminal 4 to line contact 6, to movable contact 12, to contact arm 10, to flexible braid 9, to load terminal 7.

An arc extinguishing structure is provided by generally U-shaped metallic plates 31 supported in the casing 1 at their opposite side edges 31', which rest in conforming recesses in the corresponding opposite side walls of the casing, and having centrally enlarged openings 32 providing restricted entrance portions 33. Venting holes 34 are provided in the casing adjacent the ends of the plates 31. The contact arm 10 has an intermediate portion which is adapted to move through the restricted entrance portions 33 of the openings 32 while the movable contact 12 moves through the enlarged central portions of the openings 32. The movable contact 12 is substantially greater in diameter than the thickness of the contact arm 10 at the said intermediate portion. The provision of such arc extinguishing structure and the use thereof with a contact arm having a restricted intermediate portion and an enlarged contact, forms a part of the invention disclosed and claimed in copending application Serial Number 434,472, Robert G. Page, filed June 4, 1954, and assigned to the same assignee as the present invention.

For the purpose of operating the movable contact arm between its closed-circuit position as shown in Figure 1 and its open-circuit opsition as shown in Figure 4, we provide an operating mechanism including a manually operable insulating handle 13 having an over-center tension spring 14 attached thereto at one end and supported for arcuate sliding movement in the casing by the engagement of side flange portions 13a in tracks or grooves 135 in the casing and cover, respectively. The other end of spring 14 is attached to a pin 15, which forms the knee of a toggle assembly. The toggle assembly includes an upper pair of toggle links 16 each having one end thereof pivotally supported in the insulating casing by projections 17 set in recesses therein, and having the other end journalled on pin 15. The lower part of the toggle is formed by a pair of toggle links 18 each of which is journalled on the pin at one end in common with the lower end of the links 16, and on the pin 19 at its other end. An extension 16a of each of the links 16 is provided with a flange 27 which engages a corresponding one of the lower toggle links 18 and prevents further collapse of the toggle in the over-set direction. The pin 19 passes through an enlarged opening 20 in the contact are 10, and is provided with a resilient connection with the contact arm 10 by a generally U-shaped spring 21 in accordance with our invention, in a manner to be described.

When the manual operating member 13 is in a clockwise position as shown in Figure 1, the operating spring 14 holds the toggle linkage in the over-set position as shown, holding the contact arm in the closed-circuit position. When the manual operating member 13 is moved to the left in a counterclockwise position, the line of action of the operating spring 14 crosses the axis of pins 17, and moves the toggle linkage with a snap action to the collapsed position as shown in Figure 4. As this action takes place, the pin 19 moves to the upper end of the opening 20 and thereafter serves to transmit the opening movement of the toggle to the contact arm, moving the contact arm to the ofi or open-circuit position, a stop 28 being provided in the casing to limit its travel.

Referring to Figure 2 especially, the lower toggle links 18 engage the pin 19 on either side of the contact member 11). The pin 19 has portions projecting beyond the links 18 and provided with grooves 25, at which points it rests on the opposite side portions of the wire spring 21 intermediate the bight portion 22 and the ends 24, the spring 21 being bent slightly at these points. The bight portion 22 of spring 21 rests in a notch 23 in the upper edge of the contact 'arm 10, and the ends 24 are coiled around the pin 11 at either side of the contact arm 10. In ad dition to anchoring the spring 21 on the pin 11, the coiled portions 24 also serve as spacers to centrally locate the contact arm 10 on the pin 11 between the side walls of the casing.

When the manual operating handle 13 is moved from the off to the on or closed-circuit position, the movable contact 12 engages the stationary contact 6 before the toggle links 16 and 18 have reached their fully-set position. This intermediate position is indicated in dotted lines in Figure 1. In moving the remaining distance to the on position, i. e., from the dotted line position to the fully straightened position, the toggle linkage moves the pin 19 downwardly a small amount in the slot 20. Since the movable contact 12 is already in engagement with the stationary contact 6, this downward movement of pin 19 is taken up in a bending of the spring member21 as indicated in dottedand full-line positions in this figure. In the course of this bending of spring 21, the distance between the bight portion 22 and the coiled ends 24 is shortened. Since the pin 11 is fixed in the casing as previously mentioned, the shortening action described causes the bight portion 22 of spring 21 to move slightly to the left as indicated, drawing with it the contact arm 10 by reason of its engagement at notch 23, and providing the desired contact wiping action. The spring 21 also furnishes the required resilient contact pressure when it is in the deformed position as shown in solid lines in Figure 1.

It will be observed that when the interrupter is in its full on position, as indicated in solid lines in Figure 1, the toggle links 16 and 18 have passed beyond the dead center or fully straightened condition and are slightly over-set. As this over-travel takes place, the pin 19 moves slightly in a reverse or upward direction, slightly relaxing the pressure on spring 21 and causing it to straighten a small amount, resulting in a second wiping movement in the opposite direction.

Thus the movable contact makes contact with the stationary contact by movement essentially perpendicular to the face of the stationary contact, then slides slightly in one direction (toward the pivot of the contact arm 10) and then slides slightly in the reverse direction. It will be appreciated that the last-mentioned reverse sliding action is less than the first-mentioned sliding action by an amount proportional to the vnet distortion of the spring 21 between its unstressed position and the position it occupies when the interrupter is fully on.

In addition to the double wiping action on closing of the contact, our invention provides a similar double wiping action during opening movement of the contacts. When the handle 13 is moved to the ofli position the toggle linkage is first moved to its dead center or fully straightened condition and then to its collapsed condition. As this occurs, the contact 12 moves first to the left as viewed in Figure 1, and then to the right before moving to the open position. In other words, the sequence of sliding actions obtained in closing is exactly reversed in the opening operation. I

The assembly provided by our invention also makes possible an extremely compact yet rugged and heavyduty circuit interrupter contact arm structure. The contact arm 10, for instance, is preferably made of a grade of copper of high electrical conductivity. Its construction, i. e., generally flat sheet stock mounted edgewise, gives a large amount of strength for a comparatively small cross-section, and in addition makes it suitable for use with are extinguishing structures of the type disclosed in the above-mentioned application. Being of flat sheet metal stock, the contact arm is also easily fabricated, by simple manufacturing operations. The wire spring 21 used with it is also inexpensive, easy to assembly and reliable.

While we have illustrated one embodiment of our invention, it will be understood that various modifications and applications thereof may be made, such for instance as the use thereof in automatic circuit breakers, etc., and we intend to cover all such modifications as fall within the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A circuit interrupter comprising a casing, a first contact in said casing, a second contact in said casing having a surface adapted to engage a surface of said first contact, an elongated contact arm carrying said second contact, means supporting said contact arm for movement in said casing between open and closed contact positions and also for sliding movement in a direction gen erally parallel to said contact surfaces when in engagement, a resilient member attached at one point to said contact arm and at another point to said casing, said points of attachment of said resilient member lying on a line generally parallel to said contact arm in a lengthwise direction, and means for applying force to said resilient member intermediate its said points of attachment to said casing and said contact arm to deform said resilient member and effect relative movement of said contacts generally parallel to said contacting surfaces when in engagement. I

2. A circuit interrupter comprising a casing, a first contact in said casing, a second contact in said casing having a surface adapted to engage a surface of said first contact, an elongated contact arm carrying said second contact at one end thereof, means supporting said contact arm at its other end for pivotal movement between open and closed contact positions and also for sliding movement in a direction generally parallel to said contacting surfaces when in engagement, an elongated resilient member attached at one point to said contact arm and at another point to said casing, said points of attachment of said resilient member lying on a line generally parallel to said contact arm in a lengthwise direction, and means for applying force to said resilient member intermediate its said points of attachment to said casing and said contact arm to deform said resilient member and alter the distance between said points of attachment to cause relative movement of said contacts generally parallel to said contacting surfaces when in engagement. I

3. A circuit interrupter comprising a casing, a first contact in said casing, a second contact in said casing having a surface adapted to engage a surface of said first contact, an elongated contact arm carrying said second contact, means supporting said contact arm for movement in said casing between open and closed contact positions and also for sliding movement in a direction generally parallel to said contacting surfaces when in engagement, an elon- 6 gated generally U-shaped resilient member having its bight end connected to said contact arm and having its opposite end connected to said casing, said points of connection lying on a line generally parallel to said contact arm in a lengthwise direction the legs of said U-shaped resilient member being one on each side of said contact arm and extending generally parallel to said contact arm, and means for applying contact closing force to said resilient member at a point intermediate its said ends to deform said resilient member and alter the distance between said connected ends to cause relative movement of said contacts in a direction generally parallel to said contact arm.

4. A circuit interrupter comprising a casing, a first contact in said casing, a second contact in said casing having a surface adapted to engage a surface of said first contact, an elongated contact arm carrying said second contact, means supporting said contact arm for movement in said casing between open and closed contact positions and also for sliding movement in a direction generally parallel to said contact surfaces when in engagement, a resilient member connected between said contact arm and said casing, said points of connection lying on a line generally parallel to said contact arm in a lengthwise direction and means comprising a toggle linkage connected to apply contactclosing force to said resilient member intermediate its points of connection with said casing and said contact arm and operable over-center to deform said resilient member and effect relative reciprocating movement of said contacts generally parallel to said contacting surfaces when in engagement.

5. In a circuit interrupter, a first contact, a second contact movable relative to said first contact, an elongated contact arm carrying said movable contact at one end thereof and movable between open and closed contact positions, means supporting the other end of said contact arm for pivotal and slidable movement, a generally U- shaped elongated resilient member having its bight pivotally supported on said contact arm, the legs of said U extending along either side of said contact arm and generally parallel thereto, the ends of said U being pivotally supported on either side of said contact arm at a point adjacent the other end of said contact arm, and means for applying contact-closing force to said U-shaped resilient member at a point intermediate said bight and said ends.

6. In a circuit interrupter having at least two relatively movable contacts, means including a manually operable handle movable between open and closed positions for moving said contacts into and out of engagement with each other in a direction generally perpendicular to the engaging surfaces of said contacts, and means operatively interconnected with said contact moving means for sliding said contacts against'each other first in one direction and then in the opposite direction during each movement of said manually operable handle member between said open and closed positions.

7. In a circuit interrupter a support, a first contact mounted on said support, a second contact mounted on said support and movable relative to said first contact between on and off positions, a relatively rigid contact arm pivotally and slidably supported on said support and carrying said movable contact adjacent one end thereof, an elongated resilient member supported on said support independent of said contact arm but adjacent the pivotally supported end thereof, said resilient member being connected to said contact arm at a point remote from said pivotally supported end of said cont-act arm, and means for applying contact-closing force to said resilient member at a point intermediate its connected ends, said means for applying contact force applying its greatest deforming force to said resilient member at a point intermediate the said off and on positions thereby permitting a reciprocating sliding action between the contact faces when in actual contact.

8. A circuit interrupter comprising a casing, a first contact in said casing, a second contact in said casing movable relative to said first contact, an elongated contact arm carrying said movable contact at one end thereof, means supporting said contact arm at its other end for pivotal movement between open and closed circuit positions and for sliding movement in a direction generally parallel to its length, an elongated generally U-shaped resilient member having its bight end connected to said contact arm at a point intermediate its ends and having its opposite end connected to said casing at points adjacent the said pivotally supported end of said contact arm, the legs of said U-shaped resilient member being one on each side of said contact arm, and means for applying contact-closing force to said resilient member at .a point intermediate its said ends to deform said resilient member and reduce the distance between said connected ends to cause relative movement-of said contacts in a direction generally parallel to said contact arm.

9. A circuit interrupter comprising a casing, a first contact in said casing, a second contact in said casing movable relative -to said first contact, an elongated contact arm carrying said movable contact at one end thereof and movable between open and closed circuit positions, an elongated opening in the other end of said contact member, a pivot pin fixedly mounted in said casing and passing through said opening, a generally U-shaped wire spring member having its bight seated in a recess in said contact arm and having its ends Wrapped around said fixed pivot pin on opposite sides of said contact arm and means for applying contact-closing force to said resilient member at a point intermediate said bight and said ends comprising a force-transmitting pin extending through said contact arm and across said U-shaped spring member.

10. In a circuit making and breaking device, an insulating casing, an elongated contact arm of relatively thin relatively high electrical conductivity material having a first elongated aperture at one end thereof and a second aperture generally centrally thereof, a pivot pin fixedly mounted in said casing and passing through said elongated aperture transversely to said contact arm whereby said contact arm is supported for pivotal and slidable movement in said casing, a contact-pressure spring member comprising a generally U-shaped wire spring member having its bight connected to said contact arm and having its arms extending alongside of and generally parallel to said contact arm and having its ends coiled around said pivot pin at either side of said contact arm to centrally locate said contact arm on said pivot pin, and a forcetransmitting pin extending through said generally central aperture of said contact arm and resting on opposite side portions of said wire spring member, and an electric contact member rigidly attached to said contact arm at its end opposite to said pivoted end and on an edge of said contact arm opposite to said edge having said notch therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,096,544 Jackson Oct. 19, 1937 2,521,887 Wihanto Sept. 12, 1950 2,690,486 Wilckens Sept. 28, 1954 

